Gas-Phase Reactivity of Glycosides and Methyl Glycosides with Cu +,Ag + and Pb 2+ Ions by Fast-Atom Bombardment and Tandem Mass Spectrometry

The analytical potential of the complexation of three isomeric monosaccharides (D-glucose, D-galactose, D-fructose)and two methyl glycosides (O-methyl-α-D-glucose and O-methyl-β-D-glucose)by three metal ions, Ag⁺, Cu⁺ and Pb²⁺, has been investigated by fast-atom bombardment (FAB)ionization and tandem mass spectrometry. Our results have shown that the unimolecular reactivity of Ag⁺ complexes allows the characterization of the C(4)stereochemistry of the pyranose ring, whereas a distinction between D-glucose and D-fructose is not achieved. On the other hand, each of the three [Cu + monosaccharide]⁺ complexes exhibits specific dissociation patterns. We have also observed that Pb²⁺ ions induce the richest reactivity and are of particular interest for the identification of the three isomers. Finally, this study has demonstrated that the stereochemistry of the anomeric center of O-methyl-D-glucose is easily determined by reaction with Ag⁺ or Pb²⁺ ions. Several mechanisms are proposed to account for the main fragmentations of cationized glucose.